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Background Grade groups (GGs) are an important parameter for therapeutic decision making in prostate cancer (Pca) patients. Invasive cribriform and/or intraductal carcinoma (CR/IDC) has an independent prognostic value for disease outcome, but are not included in the GG limiting their clinical use. Objective To perform a proof-of-principle study incorporating CR/IDC in the current GG. Design, setting, and participants All prostate biopsies of 1031 men with screen-detected Pca between 1993 and 2000 were reviewed for the current GG (ranging from 1 to 5) and CR/IDC. The cribriform grade (cGrade) was equal to the GG if CR/IDC was present and GG minus 1 if not. GG1 was cGrade1 if intraductal carcinoma was absent. Intervention Biopsy review for GG and CR/IDC. A total of 406 patients had received radical prostatectomy (RP), 508 radiotherapy (RT), 108 surveillance, and eight hormonal therapy, and the treatment was unknown for one patient. Outcome measurements and statistical analysis disease-specific survival (DSS), metastasis-free survival (MFS), and biochemical recurrence–free survival (BCRFS) after 15.1 yr (interquartile range 10.9–19.7 yr) follow-up were compared using Harrell's C-statistic. Results and limitations The biopsy GGs were 486 GG1, 310 GG2, 104 GG3, 64 GG4, and 67 GG5; cGrade distributions were 738 cGrade1, 102 cGrade2, 91 cGrade3, 58 cGrade4, and 42 cGrade5. The cGrade had a better discriminative value than the GG for DSS (C-index 0.79; 95% confidence interval 0.74–0.83 vs 0.76; 0.71–0.82) and MFS (0.79; 0.74–0.84 vs 0.77; 0.72–0.82). The discriminative value for BCRFS after RP and RT was similar for both models. Different diagnostic, such as use of sextant biopsies, and therapeutic strategies in the 1990s are the limitations of this study. Conclusions The cGrade is a simple Pca grade modification with better discriminative values for DSS and MFS than the GG, particularly impacting decision making in men with current GG2 Pca. Patient summary Microscopic grading is an important factor for decision making in prostate cancer (Pca) patients. We show that a simple grade modification better predicts Pca outcome and might improve treatment choices.